1. Field of the Invention
This invention relates to a GLOBAL POSITIONING SYSTEM (GPS) for motor vehicles which receives rf signals from artificial satellites (hereinafter referred to simply as the satellites).
2. Description of the Prior Art
Conventional GPS for motor vehicles is equipped with a single antenna to receive rf signals from satellites.
Since the antenna is mounted on the outside of a vehicle, e.g. on an outer wall of a roof of the vehicle, the conventional GPS has such a problem that it will degrade the external appearance of the vehicle. On the other hand, when the antenna is mounted inside of the vehicle, the antenna will not debase the outside appearance of the vehicle, but the roof and columns of the vehicle will disturb radio propagation. That is, rf signals usually receivable outside of the vehicle can not be properly received inside of the vehicle where only a single antenna is employed.
The Japanese laid-open Patent Applications Nos. 62-267899, 1-314982, and 1-318982 disclose diversity type GPS in which that two antennas are mounted inside of the vehicle. In this diversity type GPS in which only one antenna is selectively used at one time. Therefore, the system functions merely equally as the system equipped with one antenna on the outside of the vehicle, having no advantage of use of the two antennas.
In this type of GPS, since rf signals from three or four space satellites are received to determine a present position of a vehicle, it is necessary to quickly catch the rf signals from the satellites.